Are Implant Bone Loss Predictors Act Constantly Across Long-Term Function?

Methods: A retrospective cohort study design was used. The cohort was patients receiving implant therapy between January, 1996 and June 1998, at a private surgical center. Data concerning participants' demographics, implant characteristics, early surgical complications, clinical and radiographic status at the last follow-up, were collected. The outcome variable was the classification of implants into successful (MBL<0.2mm/year) and non-successful. Conditional density plots were analyzed for revealing possible relation between success and time of functioning. Forward stepwise regression analysis was used to detect the most important predictors. Finally, Clustered Logistic Regression with generalized estimation equation was used, in order to assess the magnitude of the predictors. Results: The study population consisted of 256 patients, with 936 implants and follow-up time of up to 145 month. After excluding patients with follow up<12 month, 195 patients were left with 725 implants. Graphical analysis revealed that functioning time act as possible protective factor for MBL, with temporary sharp break around 5 years of service. For implants with follow-up time<5 years the only significant predictor was the function time (OR=0.926, P<0.01). For implants with follow-up time>5 years, significant risk factors (P<0.05) were: HA coating (OR=2.438), TPS coating (OR=8.372), cigarette smoking (OR=4.743) and early surgical complications (OR=2.244). Protective factors were function time (OR=0.981) and implant diameter (OR=0.347).

Conclusions: The functioning time has a protective effect concerning MBL around implants. Risk factors do not act constantly during a long time of functioning, and therefore implants should be followed as long as possible.